1. Field of the Invention
This invention relates to a method of unloading a so-called used catalyst or the like deteriorated in activity from columns and vessels such as a hydro-desulfurizing reaction column, hereinafter referred to as "reactor", in a chemical plant such as a petroleum refining plant.
2. Description of the Prior Art
In general, various catalysts are used in reactors in chemical plants and the like. It is necessary to unload these catalysts from the reactor because of decreased activity caused by poisoning due to accumulated coke, which can result in the catalyst metal and the like, being broken to pieces due to decreased mechanical strength, repair and inspection of equipment.
The time required to unload the catalyst unloading work is needed to make as short as possible in order to minimize the period of down time of the plant operation. Furthermore, many catalysts are used under a reducing atmosphere. When the catalyst is exposed to the atmosphere for unloading the catalyst, therefore, there is a possibility of combustion and the like by heat due to oxidation of coke, sulphur and the like accumulated on the catalyst during its use. Moreover, a proper unloading procedure should be performed while avoiding the adverse influence to the human bodies by SO.sub.x generated by the combustion, the adverse influence to the human bodies by dust of the catalyst, and the like.
In relatively small-sized reactor, in unloading a catalyst, the catalyst is first completely burned and regenerated by use of steam and air in the reactor and a thereafter, the catalyst is unloaded. However, according to this method, because burning and regenerating of the catalyst are performed in the reactor, it takes a long period of time to regenerate the catalyst, thus raising the regenerating cost, and, expenses associated with controlling the pollution caused by SO.sub.x due to regeneration of the catalyst and so on. In large-sized reactors, in order to avoid combustion and the like due to oxidation of the catalyst, nitrogen gas is fed into the reactor and the catalyst is unloaded under this nitrogen gas atmosphere, or the catalyst is wetted with gas oil and unloaded during shut-down of the operation without being oxidized.
However, in the method of unloading the catalyst under the nitrogen gas atmosphere, it is technically difficult to shut off air completely during the catalyst unloading procedure and the catalyst is heated slowly and oxidizes with time due to flowout and the like of air from an air line mask worn by a worker. Moreover, the temperature in the reactor is greatly raised during the catalyst unloading technique, the environment becomes deteriorated due to generation of gas such as SO.sub.x and dust, there is a possibility of combustion. Hence, this method need not necessarily be the satisfactory method of unloading the catalyst. Where attempts have been made, for example using the method of wetting the catalyst with gas oil and unloading the same, to make the gas oil pervade whose surface of the catalyst the results have not been satisfacory in that a complete coating film over the surface of the catalyst has not been obtained.